When I make vegetable stew in my crockpot; I put some virgin olive oil on the bottom.
I then layer the following ingredients:
thinly sliced onions and garlic
thinly sliced potatoes
thinly sliced carrots
green beans
frozen corn
frozen peas
frozen cauliflower
frozen broccoli

I let this cook on low for about six hours. I use salt, pepper and garlic powder as my spices